Considerable waste is involved with the manufacture, use and discontinued use of asphalt based products such as roofing materials, including roofing shingles and rolled roofing membranes. For example, each new roofing shingle manufactures has cutout tabs that are removed and discarded. Old shingle materials removed from old buildings also add to a significant amount of roofing material waste. Indeed, it is estimated that approximately $400 million dollars are spent annually in the US alone on dumping fees for old asphalt based roofing products. Further, these old roofing materials are then buried in a landfill presenting a permanent environmental problem.
Waste generated from both new and used roofing materials such as asphalt shingles presents a significant environmental concern because of the composition of the roofing material. Typical shingles are composed of a paper or mat saturated with asphalt, an asphalt coating on the paper or mat, and granules disposed on the coating. Such materials have typically required complex recycling processes. Used roofing materials are recyclable because during the aging process, the asphalt oxidizes and merely looses its pliability. All that is needed to re-use and recycle this used asphalt is to add virgin, non-oxidized asphalt, such as flux or aromatic rich asphalt, or other material such has solvents or oil, to "re-juvenate" the old oxidized asphalt.
Past attempts at recycling asphalt shingles have failed for many reasons. For example, the prior art recycling systems have failed to reduce the shingle granules to a size small enough for the recycled shingle material to be reused in a standard roofing material manufacturing plant. If the granules in the recycled shingle material are not reduced to a fine granulation (less than approximately 50 mesh), the granules will not remain suspended in an asphalt solution cannot be pumped, and/or the recycled shingle material cannot be reused in roofing or other products which use asphalt which is pumped to the manufacturing site from a storage container, unless constant high speed agitation of the solution is provided.
Some past methods of recycling asphalt roofing material have used milling machines, such as rolling mills, bag mills, hammer mills, saw mills, etc. to produce a recycled roofing material which can be used only in road construction or as other similar "filler" material. However, merely milling the shingle material in a reduction mill without further processing has been unsuccessful in reducing the granules in the shingle material to a fine mesh so that the recycled asphalt can be reused in roofing products.
Further, such prior art systems fail to allow large and irregularly shaped pieces of used roofing material to enter the mill, while also accounting for the handling and discharge of unwanted debris such as nails, rocks and sticks.
One such apparatus for recycling roofing shingles is disclosed in U.S. Pat. No. 4,706,893 to Brock. This apparatus includes a hammer mill that comminutes the shingles and a vessel that subsequently dries then mixes the recycled shingle material with a liquid asphalt for recycling as an asphalt paving composition. This milling process will not reduce the granules in the shingle material to a small enough size for the shingle material to be reused in applications other than an asphalt paving composition. This apparatus also must be cooled and wetted to keep the shingles from sticking to the hammers.
Another shingle reducing apparatus is disclosed in U.S. Pat. No. 5,385,426 to Omann. This complex apparatus includes a shredder, two hammer mills, and two heated vessels for drying the shingle material after it has been reduced. This apparatus further requires spraying the shingles with water prior to entering the first hammer mill. This extremely complex and involved process requiring two hammer mills also is not capable of completely reducing the granules in the recycled shingle material to a fine mesh or powder. Moreover, removing the water that is introduced is expensive since the water must be boiled off before use.
One reason milling machines have been unsuccessful in reducing the granules in the recycled shingle material is because the shingle material was not heated as it was milled. In the past, heating the milling machine as the shingle material is milled was considered hazardous because of pressure build-up in the closed milling vessel or heating vessel as a result of moisture in the shingle material. Heating would also make hammer mills gum up and not work because the asphalt would become sticky and not flow out of the mill absent the introduction of liquefied asphalt or other liquid product to allow the finished milled product to flow out of the mill.